The present invention relates to a switching device for a parking brake and to a parking brake equipped with such a switching device, especially for commercial vehicles.
Parking brakes are known in particular as spring brake actuators of SAAR- or SAHR-type (that is, “Spring Actuated Air Released” or “Spring Actuated Hydraulic Released” respectively) and are used to actuate a brake-application device.
In Europe parking brakes for commercial vehicles are generally engaged by pulling and released by pushing a handle implemented as a lever—usually a linearly adjustable lever—disposed in the driver's cab.
In the United States, the parking-brake function or locking function is generally achieved by pulling a handle with a button into a pulled position; subsequently the parking brake can be disengaged by pushing the button inward and the handle downward.
Typically, the button to be actuated by the driver adjusts a parking-brake valve. In general, the parking-brake valve is designed such that, if the supply pressure drops below an internal set value, the button automatically springs outward and the rear axle is braked. In emergencies, the parking-brake valve can be pulled manually at any time, in order to activate the parking brake. As an additional option, a parking-brake safety valve can be provided, in order to reduce the pressure due to spring loading. Thus, release of the parking brake can be prevented until all systems have enabled release of the parking brake.
In such a switching device, whether it is actuated by lever or by button, the pressure conduits are routed into the driver's cab and complex valves are provided. In order to ensure that the handle springs out automatically, a complex design is necessitated.
Accordingly, it is desired to provide an improved parking brake and switching device constructed and arranged to ensure, with relatively little complexity, both automatic and manual movement capability of the parking brake, while at the same time retaining the features of conventional systems, i.e., the brake function in the pulled position and the brake release function in the pushed position of the actuating lever or button.